Home Do-It: Simple test can pinpoint source of moisture

Q. The concrete- block walls in our basement get quite damp and we worry about mold and mildew forming. What causes this and can we fix it?

A. Dampness on basement walls is caused by condensation or seepage or a combination of both. You can learn what’s causing your problem with a simple test.

Dry a portion of the wall with a hair dryer or heat gun. Cut a piece of aluminum foil about a foot square and tape it tightly to the dry spot. Check the foil after a couple of days. If there is moisture on the outside surface, you have condensation. Now pull off the foil and check the back; moisture there means you are getting seepage through the wall. There are treatments for both these problems, but they are not always completely successful.

The best remedy for condensation is a good dehumidifier, which can remove the water vapor from the basement air so it does not condense on cold surfaces like walls and pipes. Unfortunately, many dehumidifiers don’t work well at low temperatures. The lower the effective temperature range for a dehumidifier, the more it is likely to cost, but it is usually possible to get a unit that will function as low as 40 degrees for less than $300.

If you have seepage through the wall, the solution is more complicated. Special waterproofing paints are available that are supposed to stop seepage, but the wall must be carefully prepared for them to adhere and work well. Drylok is one well-known brand and is sold at many home centers and paint stores. A latex version with low odor is the best bet for closed areas like basements.

However, don’t expect any interior coating to solve a serious water seepage problem. Taking some steps outside can also help relieve the problem. Check rain gutters to make sure they are in good condition and that downspouts are extended enough to carry water well away from the foundation. If outside ground slopes toward the house near the foundation, some new grading might be necessary to promote better drainage away from the house. In severe cases, it might take an underground drain system, often called a French drain, to solve the problem.

Q. We have oak floors but are dissatisfied with the existing finish on them. Can we have them sanded and refinished at less cost than installing new flooring?

A. The cost of sanding and refinishing should be considerably less than the cost of installing new flooring. You can easily find out by calling a couple of contractors who do both types of work.

In some cases, floors that are marred by surface scratches in the finish might not even need to be sanded to bare wood. A do-it-yourself tool called a buffer, which can be rented at some tool-rental agencies, can be used to smooth the finish enough so that a new coat or two of finish can be applied.

Rust-Oleum’s Varathane Floor Renewal kit, which costs about $75 to $100 depending on the source, is said to be compatible with all types of floor finishes and require no sanding. The kit got mixed renews from users responding to an Amazon.com survey.